Typical photogrammetric plotter of the type in which a photocarriage is supported on way bars for movement in orthogonally related X Y directions utilize hand wheel driven screws for positioning photocarriages in both X and Y directions. Some of these early machines utilize servo motor systems for driving the screws, the screw normally being fixed for rotation about a fixed axis relative to the direction that the photocarriage is to be moved and a follower element engages the threads of the screw to actually move the photocarriage. Amount of rotation of the screw and hence the position of the follower therealong and accordingly the position of the photocarriage relatve to the optics gives an accurate measure of the position of the measuring mark relative to coordinates of the photograph. Exact parallelism between the axes of the screws, way bars and the like on both axes must always be maintained, so as to not adversely affect accuracy of the measurements and, at the same time assure relatively easy movement of the component parts. Moreover, it is difficult to provide manual manipulation of such photocarriages to permit rapid manual repositioning of the photocarriage according to the desires of the user. Other measuring systems eliminate the carefully calibrated measuring screw and provide the electronic equivalent in the form of electronic grids, or orthogonally related linear position transducers moved therealong for deriving positioning information, one part being mounted on the base and the other part mounted on the movable element which is the position to be measured. In such systems, the stage is driven by servo motors but the coupling of the driving force between the photocarriage and the supporting base has presented serious constraint problems which require high precision manufacturing and assembly so as to avoid binding constraints and, accordingly, are very expensive. Moreover, such systems do not permit slewing of the photocarriage stage to permit movement in any direction at high rates of speed.